Master Mariner is the official title of someone qualified to command a ship; the qualification is colloquially called a "Master's Ticket". The term was introduced in the mid 19th century, and is usually held by the chief officer/first mate as well as the captain). This term was in use in England from at least the 13th century. The captain of a merchant vessel is also called the master of that ship.

In the Royal Navy in the days of sail, "master" was often used as an abbreviation for the Sailing Master, the warrant officer responsible for the navigation and steering of the vessel. The position of sailing master was later commissioned and renamed the Navigating Officer. The Navigating Officer on a flagship, however, continued to be known as the Master of the Fleet until after the Second World War.

The Master's Mates were the assistants to the Sailing Master, also warrant officers, and were usually young men with family connections not quite good enough to become midshipmen who either aspired to become sailing masters themselves or to be commissioned as lieutenants, as often happened. Fletcher Christian was Master's Mate on HMS Bounty.

In the Royal Navy, in the days of sail, a ship's master was a standing officer. A ship's most senior warrant officers, those who headed the ship's technical departments, received their warrants from various Boards and Commissions. Their appointment and promotion did not lay within the Captain's discretion. The rate of all the more junior crew members did lay within the captain's discretion -- even midshipmen.

Master and Commander was the full title of the rank held by Commanders when they were first introduced into the Royal Navy, then equivalent to a major in the British Army. It was shortened to commander in 1814. The corresponding title in the US Navy was Master Commandant.